A memory card is an extension card that can be inserted into a host device such as a computer, a digital camera, or an MP3 player to extend a memory capacity of the host device. The memory card characteristically provides high speed access and large memory capacity. Recently, memory cards having tens of Mega-Bytes memory capacity have been developed. There are various types of memory cards that are currently available, including a Random Access Memory (RAM) card, a Read Only Memory (ROM) card, an Electrically Erasable Programmable Read Only Memory (EEPROM) card, and a flash memory card.
The flash memory card, which is a type of nonvolatile memory, is similar to an EEPROM in that memorized data can be erased through electrical processing. In comparison with the EEPROM where data can be erased by one byte at one time, the flash memory can erase data by a block unit. Thus, the flash memory can be used, for example, as an alternative of, or a supplement for, a hard disc drive in a portable computer.
The flash memory card, having a flash memory therein, has been widely used to store and reproduce data in devices such as MP3 players or digital cameras. Flash memory cards are also used in a digital peripheral apparatus such as flash drives. FIG. 1 is a block diagram showing a structure of a conventional flash memory card. Referring to FIG. 1, the conventional flash memory card 10 includes, for example, a flash memory 11 for storing data, and a controller 12 for controlling data access operations of writing, reading, and erasing data to/from the flash memory 11.
In the conventional flash memory card 10, a frequency of an internal clock signal remains constant irrespective of a frequency of an external clock signal of a host 20. Therefore with this conventional framework, the flash memory card cannot be controlled depending on the frequency of the external clock signal. As a result, maximal efficiency cannot be achieved. For example, the flash memory card cannot be controlled depending on a high clock signal frequency or a low clock signal frequency.